Laminate

ABSTRACT

A primary laminate including a tabstock in which a seal laminate including a foil layer and a top foam layer, a tabstock and a plastic film stock are fed to a laminating station is provided herein. At the lamination station, a curtain of polymeric adhesive is extruded between the plastics film stock and the top face of the primary substrate, which is partly comprised of the top face of the tabstock and partly comprised of the top foam layer of the seal laminate. Use of primary laminates obtained by such a process to form seals for sealing a container, for food or drink stored at low temperatures, is also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of prior application Ser. No.12/519,887, which is a U.S. national phase application filed under 35U.S.C. § 371 of International Application PCT/US2007/087520, filed onDec. 14, 2007, which claims priority from European Application06126645.8, filed Dec 20, 2006, which are all hereby incorporated hereinby reference in their entirety.

FIELD

The present invention relates to a method for producing a laminate whichis used in container closure systems.

BACKGROUND

It is commonplace in the packaging of a wide variety of materialsranging from pharmaceutical products to instant coffee that a closure isprovided in the form of a seal connected to the neck of a container anda screw cap covering and protecting the seal which provides are-closable cap after the seal has been removed to gain access to thecontainer. Often the closure is designed such that the underside of theseal has a heat sensitive adhesive coating or a meltable plastics layercovered by a metal foil. The seal is placed against the neck of acontainer and sandwiched against it by the applied screw cap. Uponinduction heating, the metal foil is heated which activates the heatsensitive adhesive layer or melts the plastic layer so that on cooling,the seal bonds to the neck of the container.

A problem encountered with such seals is a difficulty in removing theseals from containers. In this regard, this has been overcome byincluding a tab extending sideways from the neck of the container whichmay be gripped by the consumer to facilitate removal of the seal. Anexample of such a system is the so called “Top Tab” structure which isdescribed fully in U.S. Pat. No. 4,961,986. This system includes amultilayer substrate which is partly delaminated to provide a tab lyingusually within the circumference of the container neck. In U.S. Pat. No.4,961,986 this is achieved by forming the substrate from multiple layerswhich are adhered together across only a part of their extent. U.S. Pat.No. 4,961,986 further describes that the screw cap may include some formof liner in addition to the seal material. In such a two componentsystem, wherein the seal and liner are provided separately, is that thetwo components have to be fitted in two separate operations.

As this is expensive and increases the complexity of the fittingprocess, there has been a focus on the development of a one componentseal and liner system which avoids the need for two separate fittingoperations. For example, EP-A-1472153 describes a one component seal andliner system, for attaching into a screw cap, which includes a tab. Inthe product detailed, the seal portion of the system is adhered to theliner portion by means of a release layer such that the seal and linerrelease from each other with a peel strength in the range from 20 to 90g at a rate of 1500 mm/min on a sample strip 25 mm wide.

A further tab system is the successful “Lift “n” Peel”® commercialsystem. This can be comprised of a primary seal and a secondary liner orjust a primary seal and is usually just a primary seal. The tab isformed by interposing a layer of polyethylene terephthalate into theprimary seal which extends only over a portion of the surface area ofthe liner. The layer of polyethylene terephthalate is interposed betweenthe foam layer and top EVA/PET layer. On heating, the EVA adheres to theinterposed layer, and portion of foam still exposed and thus by virtueof the interposed plastics layer a tab, lying wholly within theboundaries of the liner, is formed.

In WO 97/02997, a method for including a tab in a primary seal laminateis disclosed. In this case three feeds are passed to a chill roll incontact with a nip roll. The first feed which will form the top layer ofthe primary seal laminate, is an ethylene-vinyl alcohol barrier layersandwiched between two polypropylene layers. The second feed is adeadening member which may be PET and the third feed is extrudedtabstock e.g. polypropylene, which forms a layer across the entire widthof the laminate forming the top layer. All three feeds come into contactat the point where the chill roll and nip roll are in contact. The chillroll quenches the extruded tabstock maximising its amorphous propertiesand causes lamination of all three layers.

A problem which can be identified with such systems is that in attachingthe system including the tab to a container to be sealed, an unevenlevel of bonding to the container is achieved with there being apropensity for stronger bonds to be formed under the tabbed portion ofthe liner as compared to the non-tabbed portion. There is a furtherdanger that on heating a metal foil of an induction system, the toplayer of the seal may burn where the heat transferred to this layer istoo great.

A further problem encountered with such seals is that when used oncontainers which are to be stored at low temperatures, for example, indairy applications, after storage at such temperatures, the bond betweenthe seal substrate and tab has a tendency to fail. This means that whenthe seal is removed from the container on opening, because the bondfails, the tab comes away from the seal substrate leaving the sealsubstrate adhered to the container rather than removing the sealsubstrate from the container.

It is therefore clear that there is a need for a simple and costeffective method for including a tabstock in a primary seal laminatewhich solves the problems of requiring producing an effective tab andachieving an even level of bonding to the container to be sealed.

SUMMARY

In this regard, the present invention provides a method for producing aprimary laminate including a tabstock comprising the steps of:

(a) feeding a seal laminate including a hot melt adhesive layer, a foillayer and a top foam layer to a laminating station;

(b) continuously feeding a tabstock, which is narrower than the seallaminate, towards the laminating station such that the bottom of thetabstock and the top foam layer of the seal laminate come intonon-adhesive contact to form a primary substrate, the top face of whichis partly comprised of the top face of the tabstock and partly comprisedof the top foam layer of the seal laminate prior to reaching thelaminating station;

(c) continuously feeding a plastic film stock which has top and bottomsurfaces to the laminating station so the bottom surface of the plasticfilm stock is in contact with the top face of the primary substrate and

(d) continuously extruding a polymeric adhesive which is a copolymer ofethylene and an alkyl(alk)acrylate having a melt flow index 1 to 10dg/min (190° C., 2.16 kg) between the top face of the primary substrateand bottom surface of the plastic film stock such that the two areadhered together.

The bond strength between the top foam layer and the plastic film stockis preferably greater than 15N/12.5 mm at 330 mm/min when the laminatingplastic film and tabstock is pulled at 90° to the longitudinal edge ofthe tabstock from the seal laminate with a separation angle of 180°. Inthe present specification reference to upper and lower surfaces ofcomponents refers to the orientation of the components in the sealformed from the laminate when the seal is in use on a container in theupright position.

The apparatus required for the method of the present invention must haveseparate unwind stations for the laminate feeds that are arranged toenable simultaneous unwinding. The laminate feeds are fed to alamination station comprising a nip between two rollers. At this pointthe feeds are adhered to each other to produce the primary laminateincluding a tabstock. The adhesive is applied vertically downwards as acurtain into the nip where the feed rollers are in contact. The speed ofthe feed rollers which form the nip should be faster than the rate ofapplication of adhesive to avoid build up of the molten adhesive in thenip which might result in an uneven coating. The adhesive is applieddirectly from the die head of an extruder.

The top layer of the seal laminate is a foam layer. It has been foundthat the inclusion of a foam layer is important in order to ensure thatan even seal to the container ultimately to be sealed is achieved. Morespecifically, this foam layer has a cushioning effect such that there isan equalisation of the pressure that is exerted around the circumferenceof a vessel closing assembly cut from the laminate in the cap fitted onto a container as induction heating takes place to adhere the liner tothe neck of the container. Thus the difference in thickness of thenon-tabbed portion as compared to the tabbed portion, does not result ina difference in the strength of the bond formed under these portions.That is to say that a substantially uniform bond strength between thelaminate and neck of the container is obtained around the wholecircumference. The foam layer also serves the purpose of providingintegrity and stiffness to the structure.

The foam may comprise several layers e.g. of coextruded materials havingsurface layers selected for compatibility with adjacent surfaces. Thefoam is preferably formed of lower alkene polymers and copolymers,preferably of ethylene and/or propylene. Foam formed from blendedpolymers may be used. Each of several layers may be formed of the samepolymers, blended in different ratios. The foam layer may be a voidedmaterial formed by stretching polymer containing particulate material.The polymer may in these voided films, comprise polypropylene.Preferably the film is formed by including foaming agents such asdissolved gases, volatile compounds or chemically reactive compounds.

Preferably the foam layer is a pure foam and is comprised of medium orhigh density polyethylene (MDPE or HDPE). In order to avoid potentialoozing of the extruded polymeric adhesive through the structure, it ispreferred that the foam has a closed cell structure. In a preferredembodiment, the foam layer is formed from a high density foam. In aparticularly preferred embodiment, the foam has a density in the rangefrom 0.5 to 0.8 g/ml preferably in the range 0.55 to 0.75 g/ml, mostpreferably in the range 0.6 to 0.7 g/ml.

In a preferred embodiment of the present invention, the foam layer has athickness in the range from 75 to 300 μm. In order to be suitable for aseal as described herein, the foam layer needs to exhibit a reasonabledegree of flexibility.

The key issue with regards to the foam is the PE make up. If theproportion of LDPE is too great then the melting point as determined byDSC will be too low. This will lead to the foam melting on inductionsealing, thus leaving a ring of exposed aluminium around thecircumference of the seal. The melting point of the preferred foam is129° C., and the melting point is preferably at least 120° C., morepreferably at least 125° C., for instance at least 128° C.

The foil and hot melt adhesive layer of the seal laminate areconventional for induction sealing systems. The hot melt adhesive issuitable to form an adhesive seal to a food or beverage (i.e.comestible) container, for instance having a peel strength between 3 and6N when peeling the liner from the container at 45° at room temperature.

It is preferable that one of the components of the primary laminate isprinted. This can be achieved in one of two ways. The tab which forms apart of the primary laminate or the plastic film stock may include aprinted layer.

As noted above, an essential feature of the primary laminate produced bythe method of the present invention is the inclusion of a tabstock sothat the seal will have a free tab. In the primary seal laminateproduced, while the relative dimensions of the tab are not limited, itmay be preferable that, for example the tab lies wholly within thecircumference of the container neck and typically the tab occupies about50% of the seal area, where the primary laminate has a diameter of lessthan 36 mm. The tab stock may be 10-100 mm wide, for instance 15 to 45mm wide. The tab is provided by adhering a tab stock to the toppolyester layer of the heat sealable laminate. The tabstock which is fedto the laminating station as detailed in step (b) is narrower in widththan the heat sealable laminate.

Preferably the tabstock is formed of a polyester, more preferablypolyethylene terephthalate. In one embodiment of the present invention,the bottom surface of the tabstock which is ultimately in contact withthe top foam layer of the heat sealable laminate may be coated with arelease material, for example, silicone. This minimised the possibilitythat during the extrusion when the finished primary seal laminate isadhered to a container by induction heat sealing, of the tabstocksticking to the top foam layer. Such release coatings are not typicallynecessary, however the tabstock may further include a coloured orprinted layer formed of polyester and attached to the top surface of theother polyester layer by an adhesive tie layer.

In step (b), in one embodiment of the present invention, rather thanfeeding a single tabstock, the feed may comprise a plurality of narrowtabstocks arranged across the machine at regularly spaced apartintervals. In this way, a wide sheet of primary laminate including atabstock may be formed which can then be slit as required (in line or insubsequent operations) thus improving the efficiency of the system.

As detailed in step (c), the third feed which is fed to the laminatingstation is a plastic film stock. Preferably the plastic film is selectedfrom the group consisting of polyester, preferably polyethyleneterepthalate, polyamide, polypropylene or a composite. Most preferablythe plastic film is polyethylene terephthalate. The width of this stockis the same as or a little narrower than the width of the heat sealablelaminate. The curtain of adhesive will extend beyond the edge of theplastic filmstock, and the edge portion which forms a thicker bead iscollected on the foam side of the seal laminate for trimming andremoval, minimising waste of expensive PET.

This plastic film layer is preferably transparent in order that theprinting of the lower layers is visible to the end user. Preferably thethickness of the plastic film stock is at least 20 μm. More preferablythe thickness of the plastic film stock is in the range from 20-40 μm.In a preferred embodiment of the present invention, where the plasticfilm stock is PET preferably it has a surface layer with improvedadhesive properties for instance formed by coextrusion. Preferably theplastic film stock is corona treated on the surface which ends up as thelowermost surface in the product, this treatment taking place upstreamof the laminating station. This is done in order to ensure that the bondformed to the polymeric adhesive in step (d) is sufficiently strongExamples of suitable PET stock materials include Lumirror 10.47 which isa film that is coextruded on one side and is commercially available fromToray.

Prior to reaching the laminating station, the bottom face of thetabstock and the top foam layer of the seal laminate are brought intocontact. There is no adhesion between the two feeds. The two feeds arefed in contact with one another to the laminating station. In order toachieve this, the two feeds must approach the laminating station fromthe same side relative to the extruder. The combination of the seallaminate and tabstock in contact with each other is referred to as aprimary substrate as they are passed to the laminating station together.As the tabstock is necessarily narrower in width than the seal laminate,the top face of the primary substrate presented to the laminatingstation is formed partly of the top face of the tabstock and partly ofthe top foam layer of the seal laminate.

In the laminating station, the primary substrate is brought into contactwith the plastic film stock which is fed simultaneously to thelaminating station but from the opposite side of the curtain ofadhesive. At the point where the top face of the primary substrate is incontact with the bottom surface of the plastic film stock, the polymericadhesive is continuously extruded between the two surfaces. The resultis that the plastic film stock is adhered over the entire surface areaof the top face of the primary substrate. This means that over part ofthe width, the plastic stock will be adhered to the top foam layer ofthe seal laminate and over the remaining width, the plastic film stockwill be adhered to the top face of the tabstock. This means that in apreferred embodiment where the primary laminate is cut, the result isthen that a tab portion is formed which lies wholly within thecircumference of the seal.

The bond formed between the top foam layer of the seal laminate and theplastic film stock must have a strength greater than 15N/12.5 mm at 330mm/min when the tab formed of tabstock and plastic film stock is pulledfrom the seal laminate at 90° to the longitudinal edge of the tab (whichis the machine direction of the manufacturing apparatus) with an angleof separation of from the seal laminate 180°. This is in order to ensurethat when using the tab to remove the seal from a container, the tabplastic film remains adhered to the primary laminate upon application ofa pulling force to the tab.

The peel test is suitably carried out using a Hounsfield Tensile Tester.Each test is carried out on three samples. The samples are cut from astrip 12.5 mm wide taken across the laminate. The sample should be atleast the length of the gap between two strips of tabstock. One end ofthe sample should be cut through the tabstock close to one longitudinaledge, allowing the tab comprising tabstock and plastic film stock to beseparated from the seal laminate. The tabstock is mounted in one jaw ofthe Tensile Tester, with the seal laminate being fixed into the otherjaw. The jaws separate at an angle of 180°. A 50N load cell is utilisedfor the test. The apparatus is set so as to allow an extension of atleast 25 mm, with a speed of 330 mm per minute.

The results recorded include the “break-in force”, the force required toovercome the initial resistance to tab de-lamination. Subsequently the“running force” is measured, that is the force required to continue toseparate the tab from the seal laminate. The running force is generallysubstantially constant. For the present product, the break-in force isthe more important, since provided this is higher than the forcerequired to peel the seal from the top of the container to which it isattached, the tab/plastic film will remain adhered to the seal aspeeling starts, the force needed to continue this peeling being lower asthe seal is peeled from the container.

The peel test is illustrated schematically in FIG. 4. This shows the tabformed of tabstock 8, adhesive 9 and plastic film 10 being mounted inthe top jaw 30 of the Tensile Tester. Into the lower jaw, 31, of theTensile Tester is mounted the seal laminate components formed of foamlayer 7, foil 5 and hot melt adhesive 4. The jaws are then moved apartin the direction of the arrow, with the force required to separate thematerials at the angle of 180° being recorded. The figure is schematicwith the thicknesses heavily exaggerated.

Much research has gone into selecting a polymeric adhesive which can beextruded as described in the present method but does not suffer from theproblem of the bond formed becoming brittle when stored at lowtemperatures. Additionally, the adhesive needs to be one that has asufficiently high surface energy to adhere to plastics materials such asPET but which will not damage the metallic rollers used. In this regard,the present applicant has found that surprisingly, these problems can beovercome by selecting a polymeric adhesive which has a melt flow indexin the range 1 to 10 dg/min, preferably less than 5 dg/min (190° C.,2.16 kg by ASTM D1328). The adhesive should be extrudable attemperatures low enough to avoid damage (be melting) to the foam layer,but which have high enough peel strengths at low storage temperaturesand at room temperature to avoid delamination of the seal during removalfrom the sealed container using the adhered tab. Materials with meltpoints (ASTM D3418) in the range 70 to 100° C. and densities in therange 0.920 to 0.955 g/cm³, for instance around 0.940-0.945 g/cm³, aresuitable. Copolymers of ethylene with C₁₋₁₂ alkyl (alk) acrylate esters(e.g. acrylate or methacrylate esters), especially C₁₋₄ alkyl esters,preferably of acrylic acid, especially butyl acrylate or methylacrylate, may be used. The copolymers are random copolymers, forinstance with mole proportions of acrylate of 0.5 to 25%, especially inthe range 1 to 20%.

Suitable copolymers are available in the series 2200 Bynel range byDuPont. Others having a higher melt index which may be suitable forlaminates which will not be used at temperatures below freezing are theLotryl MA series. Preferably the polymeric adhesive has a melt flowindex of about 2 dg/min (190° C., 2.16 kg). A particularly preferredpolymeric adhesive is an ethylene methylacrylate copolymer which has amelt flow index value of approximately 2 dg/min, sold as Bynel 22E780.

In the process of the present invention, in step (d), the polymericadhesive is extruded through a die head. The die head is preferably at atemperature in the range from 300 to 330° C. The height of the die headfrom the nip is preferably in the range from 10 to 30 cm, morepreferably in the range 15 to 25 cm, e.g. approximately 20 cm. The widthof the slot is about 0.5-1.0 mm. The speed of the nip rollers at thelaminating station is preferably in the range from 20 to 100 m/min, morepreferably 50 to 80 m/min. In order that the rollers can deal with afeed which has an uneven surface due to the regions where a tab ispresent and the regions where a tab is not present, it is preferablethat the feed rollers have a shore A hardness around 70-90, for instancea Teflon coated roller pressing against a metal chill roller.

After extrusion of the polymeric adhesive, pressure is applied to theprimary laminate by chilled nip rollers downstream of the laminatingstation to facilitate adhesion. The chilled nip rollers are preferablyat a temperature of about 23° C.

In a preferred embodiment of the present invention, the coat weight ofthe adhesive layer is in the range from 25 to 45 gm⁻².

In order that any printing on the tabstock can be seen, preferably thepolymeric adhesive is transparent.

In a further aspect of the present invention, the primary laminateincluding a tabstock maybe subsequently wound onto a final rolloptionally after slitting. Alternatively slitting may be carried out ina separate step, e.g. in a separate location.

The seal stock laminate of the present invention is generally formed inwide strips. Therefore in order to form the tabs, it is necessary to cutthe wide strips of seal stock laminate into narrower strips. Thesenarrower strips can then be punched or cut to form a seal ready to beapplied to a container. The slitting of the wide strips into narrowerstrips needs to be done with precision in order to ensure that the cutsare made at the correct positions to produce the tabs. The seal can thenbe punched from the narrower strips from the slitting step and fixedinside the top of a screw cap. This may be carried out in a procedureand/or location separate to the method of making the seal stocklaminate. The container to which the seal is attached may be made ofglass or plastic material such as polyethylene, polyester, polyvinylchloride, polypropylene or acrylonitrile-butadiene-styrene polymer.

A screw cap equipped with a seal as described above may be screwed on tothe open neck of a container thus sandwiching the seal between the openneck of the container and the top of the cap. The seal is then adheredvia the hot melt adhesive on the lower surface of the laminate to theopen neck of the container by induction heating.

As has been described above, one of the aims of the present invention isto provide a primary laminate including a tab which produces a seal thatcan still be effective even after prolonged storage of the laminate atlow temperatures. In this regard, the present applicant has developed arigorous test for determining whether a given seal is likely to fail atlow temperatures. The primary laminate including a tabstock as producedby the method according to the present invention is cut into threesample discs to be attached to the neck of a container. Samples weretaken from three different positions on the laminate, specifically theleft hand side, middle and right hand sides. Two different types ofcontainer are tested, the first being a 1 liter polyethylene chimneytype bottle used in dairy applications and the second being a polyester150 ml so-called ‘round packer’ bottle. The samples discs were sealed tothe neck of these containers using the sealing head and conditions asshown in the table below: In the meantime, a metal plate was set up onthe base of a freezer and its temperature monitored by use of acalibrated thermometer fitted with a magnetic thermocouple.

TABLE 1 SEALS TO SEALS TO POLYETHYLENE POLYESTER SETTINGS CONTAINERCONTAINER Freezer Temperature −23 to −27 −18 to −22 (° C.) metal plateFreezer type Chest Bench Bottle used 1 l chimney 150 ml ‘Round Packer’Equipment Enercon dairy sealing Relco Lab sealing head head On torque(N) 1.5 1.2 Gap setting (mm) 8 4 (4 × 1 mm EPE spacers) Power setting75% “1” Time/speed Speed = 24 m/min Time = “1”

The samples were allowed to cool for at least 2 minutes after sealing.The caps were then removed and the bottles were placed upside down inthe freezer in direct contact with the metal plates on the base of thefreezer. The sample was allowed to stand for a minimum of 2 minutes. Theseals were then removed from the necks of the bottles while still in thefreezer. Where the whole of the seal could be removed from the neck ofthe container without any delamination of the top plastics film stockfrom the adhesive, a positive result is noted. A sample fails where theplastic layer delaminates from the foam, which can be observed assurface of the top plastic film layer is completely transparent ratherthan having foam still adhered to it. Where a sample fails it is testedagain the following day. If the problem still persists, the sample isrejected.

One advantage of seals produced by the method of the present inventionis that they can be used universally for sealing containers ofcomestibles requiring storage at low or high temperatures, even down toas low as −30° C. or as high as 30° C. The invention is of particularutility where the storage temperature is in the range 0 to 6° C.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference tothe following figures, in which:

FIG. 1 is a cross section through an example of a primary laminateincluding a tabstock as formed according to the method of the presentinvention with a vertical dimension greatly exaggerated;

FIG. 2 is a schematic diagram of the laminating apparatus used in themethod of the present invention;

FIG. 3 is a perspective view of a part of the apparatus illustrated inFIG. 2;

FIG. 4 is a cross section through a sample of the primary laminate beingsubjected to the 180° peel test to check the strength of the extrudedadhesive.

FIG. 5 is a perspective view showing the seal in place on the neck of acontainer.

DETAILED DESCRIPTION EXAMPLE 1

A seal laminate (1) comprising heat sealable (hot-melt) layer (4) foradhesion to a container to be sealed, a foil layer (5) and a top layerof polyethylene foam (7) is obtained commercially from Isco JacquesSchindler. This seal laminate is rolled onto a first feed roll (13) inthe laminating apparatus.

The second feed roll (14) in the laminating apparatus is the source ofthe tabstock, which in this case, is a layer of polyethyleneterephthalate (8). The width of the layer of polyethylene terephthalate(8) is in the range from 25-60 mm.

A third feed roll (15) is loaded with the plastics film stock, in thiscase a PET stock (10) which can be obtained commercially from Toray,Europe. The thickness of the PET stock (10) is in the range from 23-36μm. The PET stock (10) used is a co-extruded PET material available asLumirror 10.47 from Toray. The coextruded surface layer ensures optimaladhesion to the adjacent foam layer of the seal laminate.

The seal laminate (1), tabstock (8) and PET stock (10) aresimultaneously fed to the laminating station (6) where an extruder (17)is positioned vertically above the nip between rollers (18 and 19).Prior to reaching the laminating station (6), the seal laminate (1) andtabstock (8) are brought into contact to form a primary substrate (1 a).

Ethylene methyl acrylate copolymer (9) with a melt flow index of 2dg/min (190° C., 2.16 kg (ASTM D1238)) is then extruded continuously asa curtain from the extruder (17) between the top face of the primarylaminate (1 a) and the bottom face of the PET stock (10). The height ofthe die head above the nip was about 20 cm. The extrusion conditionsi.e. the weight of adhesive being extruded, its, speed and extruder headtemperature, were such that a temperature of greater than about 200° C.,for instance as much as about 250° C. is attained at the nip foradhesion. Roller 18 is a chilled stainless steel roller, while roller 19has a Teflon coated surface with Shore A hardness of 75. The rollers(18) and (19) are moving at a speed of 70 m/min relative to the speed ofapplication of the adhesive, the pressure between them selected to avoidthe curtain creasing at the nip. The bottom face of the PET stock (10)and the resulting primary laminate (1 b) including a tabstock is passedwith the bottom face of the PET stock in contact with a chill roller(18) at a temperature of about 23° C. to be rolled on to a final productroll (32). This process is illustrated schematically in FIG. 2.

The break-in peel strength was measured as explained above andillustrated in FIG. 4, of a primary laminate formed using a PET stock(10) thickness of 36 μm and a PET tabstock thickness of 12 μm onto theseal laminate upper surface of polyethylene foam, wherein the coatweight of the extruded ethylene methyl acrylate copolymer (9) was 40gm⁻². The value was greater than 15N/12.5 mm at 33o mm/min.

The coat weight was determined as follows: a 0.5 m to 1 m length ofpaper backed polyester which has a width of 1 m was passed to thelaminating station between primary substrate 1 a and resin 9. A curtainof the ethylene methyl acrylate copolymer was then extruded continuouslybetween the top polyester face of the paper backed polyester and thebottom face of the PET stock (10) under the run conditions of the line.Several 10×10 cm samples were then cut across the width of the web andtheir weight in g was recorded. The weight of the paper backed polyesterand PET stock (10) were subtracted from this figure and the result wasmultiplied by 100 to give a coat weight in gm⁻².

The seal stock laminate was then cut into narrow strips. From thesestrips, circular discs were punched to form discs of the seal stocklaminate (16) i.e. seals. The seals are fixed inside screw caps. Thescrew cap equipped with the seal is then screwed onto the open neck ofthe bottle 24. The cap and bottle are then subjected to an inductionheating step in which the foil is heated around its periphery by thegeneration of eddy currents within it, which, in turn, melts the heatsealable layer (4) to bond the seal to the open neck of the bottle.

The invention claimed is:
 1. A primary laminate comprising: a seallaminate including a heat seal layer for sealing to a container, a foillayer and a top foam layer; a tabstock which has a top and a bottom facewherein the bottom face is in contact with the top foam layer of theseal laminate; a layer of plastic film adhered to the top face of thetabstock and to the top foam layer by a random copolymer of ethylene andalkyl acrylate and having a melt flow index in the range of 1 to lessthan 5 dg/min (190° C., 2.16 kg); and wherein the random copolymer ofethylene and alkyl acrylate bonds the layer of plastic film to the topfoam layer so that the layer of plastic film does not delaminatetherefrom when subjected to a low temperature freezer test by exposing asealed container with the primary laminate to a temperature from about0° C. to about −30 to form a cold primary laminate and when applying aremoval force to the cold primary laminate for removal of the coldprimary laminate from the container.
 2. The primary laminate accordingto claim 1, wherein the random copolymer of ethylene and alkyl acrylatehas a melt point of about 70 to about 100° C. and a density of about0.92 to about 0.955 g/cm³.
 3. The primary laminate according to claim 1,wherein the random copolymer of ethylene and alkyl acrylate is acopolymer of ethylene and C₁₋₁₂ alkyl acrylate esters.
 4. The primarylaminate according to claim 1, wherein the random copolymer of ethyleneand alkyl acrylate is an ethylene methyl acrylate copolymer effective toprovide an initial peel strength between the layer of plastic film andthe top foam layer of greater than 15N/12.5 mm at 330 mm/min.
 5. Theprimary laminate according to claim 1, wherein the random copolymer ofethylene and alkyl acrylate has a melt point of about 70 to about 100°C. and the top foam layer has a higher melt point of about 120° C. toabout 129° C.
 6. The primary laminate according to claim 1, wherein thelayer of plastic film is a co-extruded polyester film.
 7. A pull-tabsealing member constructed to be secured to a rim surrounding an openingof a container, the pull-tab sealing member comprising: a seal laminatehaving a bottom heat seal layer for bonding to a rim of a container anda top foam layer; a tab having a top and a bottom face wherein thebottom face is in contact with but not bonded to the top foam layer ofthe seal laminate so that the tab lies wholly within a perimeter of thepull-tab sealing member; a layer of plastic film forming a portion ofthe tab and adhered to the top foam layer of the seal laminate by anextruded polymeric adhesive; and the extruded polymeric adhesive is arandom copolymer of ethylene and alkyl acrylate and has a melt flowindex in the range of 1 to less than 5 dg/min (190° C., 2.16 kg)effective to bond the layer of plastic film to the top foam layer sothat the layer of plastic film does not delaminate therefrom upon aremoval force applied to the tab when the pull-tab sealing member isexposed to temperatures from about −30° C. to about 0° C.
 8. Thepull-tab sealing member according to claim 7, wherein the polymericadhesive has a melt point of about 70 to about 100° C. and a density ofabout 0.92 to about 0.955 g/cm³.
 9. The pull-tab sealing member of claim7, wherein the polymeric adhesive has a melt point of about 70 to about100° C. and the top foam layer has a higher melt point of about 120° C.to about 129° C.
 10. The pull-tab sealing member according to claim 7,wherein the polymeric adhesive is a copolymer of ethylene and C₁₋₁₂alkyl acrylate esters.
 11. The pull-tab sealing member according toclaim 7, wherein the polymeric adhesive is an ethylene methyl acrylatecopolymer effective to provide an initial peel strength between thelayer of plastic film and the top foam layer of greater than 15N/12.5 mmat 330 mm/min.
 12. The pull-tab sealing member according to claim 7,wherein the layer of plastic film is a co-extruded polyester film.
 13. Apull-tab sealing member constructed to be secured to a rim surroundingan opening of a container, the pull-tab sealing member comprising: aseal laminate having a bottom heat seal layer for bonding to a rim of acontainer and a top polymer foam layer; a layer of polymer filmpartially adhered to the top polymer foam layer of the seal laminate bya random copolymer of ethylene and alkyl acrylate to form a tab definedby a portion of the polymer film layer not adhered to the top polymerfoam layer so that the defined tab lies wholly within a perimeter of thepull-tab sealing member; and the random copolymer of ethylene and alkylacrylate is a random copolymer of ethylene and C₁₋₁₂ alkyl acrylateesters with a mole percentage of the acrylate between 0.5 and 25 percentand has a melt flow index from 1 to less than 5 dg/min (190° C., 2.16kg)effective to bond the layer of plastic film to the top foam layer sothat the layer of plastic film does not delaminate therefrom upon aremoval force applied to the tab throughout a temperatures from about−30° C. to about 0° C.
 14. The pull-tab sealing member according toclaim 13, wherein the random copolymer of ethylene and alkyl acrylatehas a melt point of about 70 to about 100° C. and a density of about0.92 to about 0.955 g/cm³.
 15. The pull-tab sealing member according toclaim 14, wherein the random copolymer of ethylene and alkyl acrylate isa random copolymer of ethylene methyl acrylate in an amount effective toprovide an initial peel strength between the layer of polyester film andthe top polyolefin foam layer of greater than 15N/12.5 mm at 330 mm/min.16. The pull-tab sealing member according to claim 13, wherein the layerof polymer film is a co-extruded polyester film.